Interaction between two polyelectrolytes in monovalent aqueous salt solutions

TL;DR

This study employs the soft-potential-enhanced Poisson-Boltzmann (SPB) theory, fitted to molecular dynamics data, to accurately model interactions between two polyelectrolytes in monovalent salt solutions, revealing its effectiveness and limitations.

Contribution

The paper introduces the application of the SPB theory to polyelectrolyte interactions, validated against MD simulations, demonstrating its accuracy in the weak-coupling regime.

Findings

SPB theory accurately predicts PE interactions beyond PE radius

Positional correlations cause local asymmetries in charge and ion distributions

Short-range oscillations indicate deviations from SPB predictions

Abstract

We use the recently developed soft-potential-enhanced Poisson-Boltzmann (SPB) theory to study the interaction between two parallel polyelectrolytes (PEs) in monovalent ionic solutions in the weak-coupling regime. The SPB theory is fitted to ion distributions from coarse-grained molecular dynamics (MD) simulations and benchmarked against all-atom MD modelling for poly(diallyldimethylammonium) (PDADMA). We show that the SPB theory is able to accurately capture the interactions between two PEs at distances beyond the PE radius. For PDADMA positional correlations between the charged groups lead to locally asymmetric PE charge and ion distributions. This gives rise to small deviations from the SPB prediction that appear as short-range oscillations in the potential of mean force. Our results suggest that the SPB theory can be an efficient way to model interactions in chemically specific complex PE systems.